Voltage Space Phasor Research Articles

Power-Loss Ride-Through with Reduced Number of Voltage Sensors in a Cascaded H-Bridge Inverter fed Vector Controlled Induction Motor Drive

Cascaded H-Bridge (CHB) inverter-fed drives are quite popular in high-power industrial applications. However, these drives are extremely sensitive to power supply disturbances on the input grid side, such as voltage sags or short-duration power interruptions that cause the drive to trip on under-voltage protection resulting in production losses. Therefore, it is necessary to employ techniques that improve the resilience of the drive by enabling it to smoothly ‘ride-through’ such short-duration disturbances. The traditional ride-through solutions in CHB drives typically necessitate additional hardware or multiple DC link voltage sensors, which increase the cost and complexity of the system. This paper proposes a simple and cost-effective approach for power-loss ride-through in CHB inverter based vector-controlled induction motor drives. In this method, the kinetic energy stored in the rotating mass is recovered and fed back to the DC-link capacitors to keep all the DC link voltages constant during momentary supply interruptions or voltage sags. The proposed technique works by controlling the voltage space phasor without the need for extra hardware and voltage sensors at the CHB cells. The proposed scheme is experimentally validated on a 30 kW, 7-level CHB inverter based vector controlled induction motor drive.

Active and Reactive Power Control for Dual Excited Synchronous Generator in Wind Applications

This paper presents a dual excited synchronous generator (DESG) as a novel suitable alternative generation system for wind energy conversion systems. A new control strategy was proposed for the DESG wind turbine system. With this control technique, the DESG could be operated as a constant-speed constant-frequency (CSCF) generation system with the benefit of adjusting the reactive power or as a variable-speed constant-frequency (VSCF) generation system with the benefits of simple control methods and lower copper losses. Using the space phasor model of the DESG, a direct relationship between the electromechanical torque and the armature reactive power in terms of the field current space phasor magnitude and the field voltage space phasor angle is provided. The proposed control strategy is based on controlling the field-current space phasor magnitude and the field-voltage space phasor phase angle to regulate the active and reactive powers of the DESG. Simulation results, based on MATLAB/SIMULINK, for a 1.1 kW DESG wind turbine system have been executed to verify the introduced control technique under various operating conditions. Also, experimental studies have been carried out to validate the simulation results using the proposed control algorithm.

Fractal Approach Based Simplified and Generalized Sector Detection in Current Error Space Phasor Based Hysteresis Controller Applied to Multilevel Front-End Converters

The current error space phasor (CESP) based hysteresis controller employed for front-end converter requires two (inner and outer) hysteresis bands for vector selection and sector detection, respectively. As a result of this, the CESP moves out of the fixed (hexagonal) inner boundary many times in one fundamental cycle (and touches outer hysteresis band) to detect appropriate sector. This distorts the supply current waveform and increases the implementation complexity. To provide effective solution to the said issue, in this article, a fractal approach with a triangularization technique is proposed and analyzed to eliminate the outer hysteresis band and lookup table for sector change detection. The novelty proposed in this article is the integration of the fractal approach to CESP-based hysteresis controller, which reduces the complexity of the implementation of CESP-based hysteresis controller for any general multilevel front-end converter. The detailed analysis of the proposed technique for sector detections is presented considering the voltage space phasor structure of three-level and five-level converters. A generalized flowchart for any multilevel converter employing CESP-based hysteresis controller with proposed sector detection technique is developed and presented. Laboratory prototype is developed for a three-level flying capacitor front-end converter with an effective capacitor voltage balancing scheme. The experimental results are presented to validate the effectiveness of the proposed current controller in terms of unity power factor and low harmonic distortion in the line current under various practical conditions.

Pulse width modulation schemes enabling single DC power source driven dual two‐level voltage source inverter with single voltage source inverter switching

Three-level voltage space phasor can be obtained using a dual two-level voltage source inverter (VSI). Two zero sequence voltage elimination pulse width modulation (PWM) switching variants are proposed in this paper for complete elimination of zero sequence voltage (ZSV) in the dual-VSI scheme. Both the PWM variants are designed in such a way that only one inverter is switched at any instant of time; to ensure that switching power losses in the dual-VSI is limited to one inverter only at any instant of time. Analytical expressions for the dwell times of the dual-VSI are developed and presented that successfully forces the ZSV in the dual-VSI to zero; at all instants of time. As a result, both the PWMs facilitate the dual-VSI to be driven from a single DC power source only. The implementation of the proposed PWM algorithms is greatly simplified and involves just the use of instantaneous magnitudes of the reference space vector. The implementation of PWMs totally avoids the time consuming task of sector identification and do not use look up tables. The PWMs proposed in this paper are first analysed, simulated using MATLAB/SIMULINK and then verified experimentally to validate the proposed PWMs.

Suppression of Saturation Effects in a Sensorless Predictive Controlled Synchronous Reluctance Machine Based on Voltage Space Phasor Injections

This paper presents a digital strategy to suppress magnetic- and cross-saturation effects in a sensorless predictive direct-torque-controlled synchronous reluctance machine (SynRM). In SynRMs, the angular position of the rotor can be estimated by using inductance variations due to geometrical effects of the rotor. However, magnetic- and cross-saturation effects lead to large errors on the estimated angular position, particularly when the magnetization level and torque load change. This error deteriorates the performance of the electrical drive when the estimated position of the rotor is used instead of the measured one in a sensorless control scheme. In this paper, it is shown how saturation effects can be readily alleviated by using a digitally implemented quadrature phase-locked loop observer, together with linear regression, so that easy digital implementation, stable operation, and null parametric dependence can be achieved. The experimental results at very low and zero speeds verify the effectiveness of the proposed sensorless control scheme.

A Predictive Torque Control for the Synchronous Reluctance Machine Taking Into Account the Magnetic Cross Saturation

A predictive torque and flux control algorithm for the synchronous reluctance machine is presented in this paper. The algorithm realizes a voltage space phasor preselection, followed by the computation of the switching instants for the optimum switching space phasor, with the advantages of inherently constant switching frequency and time equidistant implementation on a DSP-based system. The criteria on how to choose the appropriate voltage space phasor depend on the state of the machine and the deviations of torque and flux at the end of the cycle. In order to obtain an appropriate model of the machine, it has been developed on a d-q frame of coordinates attached to the rotor and takes into account the magnetic saturation in both d-q axes and the cross-saturation phenomenon between both axes. Therefore, high-performance torque control is achieved, and the torque ripple is reduced. Simulated and experimental results using a DSP/field-programmable-gate-array-based control and a commercially available machine show the validity of the proposed control scheme

A Novel Split Phase Induction Motor Drive without Harmonic Filters and with Linear Voltage Control for the Full Modulation Range

A modulation scheme for a split phase (six phase) induction motor is presented in this paper. For a six phase induction motor drive harmonics of the order 6n ± 1 (n = 1, 3, 5 etc.,) will not contribute to the air gap flux and hence these harmonic currents are limited by the stator impedance only. So harmonic filters are needed for the suppression of these (6n ±1( n = 1, 3, 5 etc.,) high amplitude harmonic currents, when a six phase induction motor is used for variable speed application. In the proposed scheme, a modulation technique to eliminate the 6n ± 1 (n = 1, 3, 5 etc.,) harmonic currents, without the need for harmonic filters, from the stator phases of a six phase induction motor drive is explained. An openend winding drive configuration with appropriate DC-link voltages, is chosen in such away that a 12-sided polygonal voltage space phasor combinations are achieved for each 3-phase group, independently. A modulation scheme based on 12-sided polygonal voltage space phasors cancel the 6n ± 1 (n = 1, 3, 5 etc.,) harmonic voltages from all the motor phases and hence currents due to these harmonics can not flow in the motor phases of the six phase machine. For the same flux level of operation, nearly 11.5 % increase in modulation range is possible from this proposed drive (while still being in the linear PWM range), which is more than that of a six-step over modulation region in a conventional 3-phase induction motor drive. The proposed drive scheme is experimentally verified, for variable speed application, using a 1.5 kW six-phase induction motor drive.

Three-Level Inverter Scheme With Common Mode Voltage Elimination and DC Link Capacitor Voltage Balancing for an Open-End Winding Induction Motor Drive

A dc link capacitor voltage balancing scheme along with common mode voltage elimination is proposed for an induction motor drive, with open-end winding structure. The motor is fed from both the ends with three-level inverters generating a five level output voltage space phasor structure. If switching combinations, with zero common mode voltage in the pole voltage, are used, then the resultant voltage space vector combinations are equivalent to that of a three-level inverter. The proposed inverter vector locations exhibit greater multiplicity in the inverter switching combinations which is suitably exploited to arrive at a capacitor voltage balancing scheme. This allows the use of a single dc link power supply for the combined inverter structure. The simultaneous task of common mode voltage elimination with dc link capacitor voltage balancing, using only the switching state redundancies, is experimentally verified on a 1.5-kW induction motor drive

Sixth Torque Harmonic in PWM Inverter-Fed Induction Drives and Its Compensation

The sixth-order torque ripple harmonic in induction motors under field-oriented control with voltage space phasor modulation is investigated by means of a simulation model. It is shown that the main reason for its appearance lies in the pulsewidth modulation. Measurements on a 220-kW asynchronous drive confirm the simulation results. A compensation strategy is proposed.

Three-level inverter configuration with common-mode voltage elimination for induction motor drive

A scheme for a three-level voltage space phasor generation with common-mode voltage elimination is proposed. An open-end-winding induction motor, fed from both ends by two three-level inverters, which are realised by a cascading two two-level inverter, is used in this configuration. The voltage space vectors of individual three-level inverters, which generate the same common-mode voltage in the inverter pole voltage, are variously grouped. When these voltage space vectors are used to switch individual three-level inverters, it results in zero common-mode voltage across the motor windings. In the proposed scheme, voltage space phasors from individual inverters with zero common-mode voltage in the inverter pole voltage are used for PWM control. For the proposed drive configuration, the DC link voltage requirement is only half when compared to the DC link voltage of a conventional neutral-point-clamped (NPC) three-level inverter. The proposed inverter configuration offers reduced circuit and control complexity when compared to similar schemes with NPC or H-bridge inverter configurations.

Dual two-level inverter scheme for an open-end winding induction motor drive with a single DC power supply and improved DC bus utilisation

A dual two-level inverter fed open-end winding induction motor drive with a single DC-power supply is proposed. The proposed scheme produces voltage space vector locations identical to those of a conventional three-level inverter. In the conventional neutral-clamped three-level inverter, the series-connected DC link capacitors carry the load current, resulting in a fluctuating neutral point. Also, a three-level inverter requires bulky DC link capacitors. In the proposed scheme, the DC link capacitors carry currents of higher frequency and hence the neutral point fluctuations are reduced. A PWM switching strategy to suppress the zero sequence currents for all the voltage space phasor combinations is also proposed. This strategy is an improvisation of the one that uses a switched neutral to eliminate the triplen harmonic currents and results in an improved DC bus utilisation.

A High Resolution Multilevel Voltage Space Phasor Generation for an Open-end Winding Induction Motor Drive

A topology for high resolution voltage space generation for an open-end winding induction motor drive is presented in this paper. The open-end winding induction motor is fed from both ends by two 3-level inverters with asymmetrical d.c. links. This results in voltage space phasor levels equivalent to a conventional 9-level inverter. The 3-level inverters used in the proposed drive, are realised by cascading two 2-level inverters and do not require the neutral point clamping diodes. Compared to the H-bridge topology, the proposed scheme uses a lower number of power supplies. In the multilevel carrier based Sinusoidal Pulse Width Modulation (SPWM), used for the proposed drive, a progressive discrete d.c. bias depending upon the speed range is given to the reference wave so that the drive can operate in the i-level modes (i = 2, 3, ..9) depending on the speed range. The inverter with the higher d.c.-link voltage is switching less frequently, compared to the inverter with the lower d.c.-link voltage. The drive is implemented and tested with a 1.5 kW open-end winding induction motor and the experimental results are presented.

Multi Level Voltage Space Phasor Generation for an Open-End Winding Induction Motor Drive Using a Dual Inverter Scheme with Asymmetrical DC-Link Voltages

An open-end winding induction motor drive fed from two inverters with different DC-link voltages is proposed in this paper. A total of 64 voltage space phasor combinations are possible in this scheme, as each inverter is capable of producing 8-voltage space phasors independently of the other. The proposed scheme produces 37 voltage space phasor locations while a 3-level inverter produces only 18 voltage space phasor locations. In the proposed scheme, the neutral connection of the induction motor is removed (open-end winding) and is fed from both the ends. Two 2-level inverters with isolated DC-link voltages of 2/3 Vdc and 1/3 Vdc are used for driving the motor, where Vdc denotes the DC-link voltage of an equivalent conventional (single-inverter) scheme. A combination of two 2-level inverters with 2/3 Vdc and 1/3 Vdc DC-link voltages produces a total of 64 voltage space phasor combinations in 37 space phasor locations. The voltage space phasor locations can be associated with three regions according to the speed range. In the lower speed range, while being in the PWM mode of operation, the phase voltage exhibits a six-step envelope (similar to the conventional scheme) and in the middle range the motor phase voltage, still being in the PWM mode of operation, shows a 12-step envelope. In the higher speed range (including over modulation) the motor phase voltage has an 18-step envelope. A simple and elegant space phasor based PWM scheme has been proposed in this paper, which requires only the instantaneous values of the three phase motor reference voltages in all of the sectors. The sector identification is achieved by comparing the components of the motor reference voltages, using simple hysteresis comparators, along the three orthogonal axes to the a, b, c phase axes. The proposed PWM strategy has been experimentally verified on a 1HP open-end winding motor and the experimental results are presented in this paper.

A Space-Vector Modulation Scheme for a Dual Two-Level Inverter Fed Open-End Winding Induction Motor Drive for the Elimination of Zero-Sequence Currents

The dual two-level inverter fed open-end winding induction motor drive gives voltage space phasor locations similar to a three-level inverter fed induction motor drive. The dual inverter scheme renders advantages such as redundancy of the space vector combinations for the same number of space vector locations and the absence of neutral point fluctuations. In a dual-inverter scheme, a total of 64 space-vector combinations are distributed over 19 space vector locations compared to 27 space-vector combinations distributed over the same number of locations in a three-level inverter. The common mode voltages (the harmonics of the triplen order) need to be suppressed by transformer isolation or the use of harmonic filters. In this paper, a space vector modulation scheme for the suppression of zero sequence currents (the harmonics of the triplen order) for a dual two-level inverter fed open-end winding induction motor drive is described. The proposed scheme does not require bulky transformers or harmonic filters for the elimination of the zero sequence currents. The proposed space vector PWM is based on the observation that certain voltage space-vector combinations in the dual inverter scheme do not contribute to the triplen harmonics and hence the PWM scheme that exclusively employs these combinations is used to eliminate the triplen harmonic currents.

PWM inverter switching strategy for a dual two-level inverter fed open-end winding induction motor drive with a switched neutral

A dual two-level inverter fed open-end winding induction motor drive is proposed in this paper. A total of 64 voltage space phasor combinations are possible in this scheme since each inverter produces eight voltage space phasors. The scheme produces voltage space phasor locations similar to that of a three-level inverter except that in a three-level inverter the series-connected DC link capacitors carry the load current, which results in undesirable fluctuating voltage space phasors. Also, a three-level inverter requires a bulky DC link capacitor. In the proposed scheme the DC link capacitor carries only the ripple current and hence the voltage space phasor fluctuations are absent. A PWM switching strategy aimed at suppressing the zero sequence currents is proposed, using auxiliary switch-assisted neutral generation.

The modern space‐phasor theory, part I: Its coherent formulation and its advantages for transient analysis of converter‐fed AC machines

AbstractFour internal quantities plus the rotor position of a rotating electrical machine suffice in order to describe its dynamic behaviour. Starting from this fact, first the space‐phasor concept is introduced as an excellent analytical tool, the expressions of the main phasors are given (special attention is paid to the analysis and the physical interpretation of the voltage space phasor) and thereafter the formulation of the theory is carried out. It is then shown that all the transient states of a converter‐fed symmetrical machine can be represented by a very simple space‐phasor diagram, analogous to the one used for describing its steady state through time phasors. The diagram and the corresponding dynamic equations are deduced in a direct and immediate way, which is very useful for studies of electronically powered AC machines. The second part of this article will discuss in detail the reasons why the phasorial representation of transients is not possible neither in the “Generalized Machine Theory,” nor in the “Space‐Vector Theory” and will provide a comparison between these three theories.

Synchronous servo-drive: a compact solution of control problems by means of a single-chip microcomputer

The completely digital control of high dynamic synchronous servo-drives with rare-earth permanent-magnet (PM) disk rotor is considered. The aim was to bring the hardware of the control unit into a very small and compact form. The realized unit consists of two modules: a 16-b single-chip microcomputer including measurement value detection, set value output, and communication interfaces; and a MOSFET voltage source inverter controlled by pulsewidth modulation techniques. Due to the structure of the digital system, several control strategies were realized and compared: a mathematical model of the PM synchronous motor was derived, methods of voltage space phasor generation were found, and digital control algorithms without the support of any analog feedback circuits were implemented. A position feedback controller was realized. Results of the digital simulation and of the practical plant are given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dynamic measuring of frequency and frequency oscillations in multiphase power systems

Instantaneous system frequency is defined, and a method of frequency measurement is proposed which determines the angular velocity of the rotating voltage space phasor. Impulses in frequency caused by steps in phase are blanked out, whereas harmonics and noise are suppressed by FIR filters. Using an optimized observer-based filter, frequency modulations are split into and frequency drift and frequency oscillation signals, which can be used in power control and power system stabilization.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>